CN112830704A - Shrinkage reducing agent for ultrahigh-performance concrete and preparation method thereof - Google Patents

Abstract

The invention discloses a shrinkage reducing agent for ultra-high performance concrete and a preparation method thereof. The preparation method comprises the following steps: (1) esterification: carrying out esterification reaction on maleic anhydride, polyethylene glycol substances and polypropylene glycol substances under the action of a catalyst to obtain a compound A solution; (2) polymerization: respectively dropwise adding persulfate solutions into the solution A, and controlling the reaction temperature to be 50-60 ℃ for reacting for 1-4 hours; (3) neutralizing: and after the reaction is finished, cooling to room temperature, and adding alkali to adjust the pH value of the solution to 6-7 to obtain the shrinkage reducing agent for the ultra-high performance concrete. The shrinkage reducing agent for the ultrahigh-performance concrete has an obvious effect of inhibiting early plastic shrinkage of the concrete, is low in mixing amount and has no obvious influence on the setting time, and can be used together with a polycarboxylic acid water reducing agent.

Description

Shrinkage reducing agent for ultrahigh-performance concrete and preparation method thereof

Technical Field

The invention relates to the technical field of concrete admixtures, in particular to a shrinkage reducing agent for ultra-high performance concrete and a preparation method thereof.

Background

The ultra-high performance concrete (UHPC) has excellent mechanical property and durability, can meet the development of modern engineering structures towards higher, longer and lighter directions, and is widely accepted by experts and scholars at home and abroad at present in large-span bridge structures and thin-wall structures. Due to the characteristics of low water-gel ratio, large using amount of cementing materials, high proportion of mineral admixture, low mixing amount of coarse aggregate and the like of UHPC, the UHPC is accompanied with larger self-shrinkage in the coagulation hardening and after-hardening service process. Internal stresses due to shrinkage can exacerbate the risk of cracking the concrete member, affecting its durability. How to effectively control the shrinkage of UHPC and improve the application performance of UHPC is widely concerned at home and abroad.

The shrinkage reducing agent has a good effect of reducing the shrinkage of concrete, is one of effective measures for preventing the generation of cracks on a cement-based material, and reduces the water evaporation of a solution by reducing the surface tension of a capillary solution in the concrete, thereby reducing the shrinkage stress of the concrete and improving the cracking problem of the concrete. At present, the shrinkage reducing agent for cement-based materials mainly comprises micromolecular alcohols, ethers and organic alcamines. The alcohol shrinkage reducing agent comprises secondary alcohol, tertiary alcohol and homologues thereof, and the alcohol shrinkage reducing agent has the advantages of low boiling point, easy volatilization, flammability, inconvenient use in engineering practice, large mixing amount and heavy retardation; the ether shrinkage reducing agent mainly comprises glycol ether, polyoxyethylene alkyl ether and the like, which have relatively good shrinkage reducing effect, but most of the ether is volatile, has pungent smell, is harmful to the health of operators, and has compatibility problem with the polycarboxylic acid water reducing agent; alkanolamine reducers are expensive and have limited application.

Disclosure of Invention

The invention provides a shrinkage reducing agent for ultrahigh-performance concrete and a preparation method thereof, aiming at the problems that the traditional small-molecular shrinkage reducing agent is high in mixing amount and heavy in retarder, influences the strength of the concrete and is poor in compatibility with a polycarboxylic acid water reducing agent.

The shrinkage reducing agent for the ultrahigh-performance concrete is prepared by taking maleic anhydride, polyethylene glycol substances and polypropylene glycol substances as raw materials and performing esterification and polymerization reaction, wherein the molar ratio of the maleic anhydride to the polyethylene glycol substances to the polypropylene glycol substances is 1:1: 0.2-1: 2: 0.5.

The polyethylene glycol substances are polypropylene glycol and derivatives thereof. Preferably, the solvent is one of polyethylene glycol, polyethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and triethylene glycol monomethyl ether.

The polypropylene glycol substances are polypropylene glycol and derivatives thereof. Preferably, the polypropylene glycol is one of polypropylene glycol, polypropylene glycol monomethyl ether, dipropylene glycol monoethyl ether and dipropylene glycol monobutyl ether.

The catalyst is one of sulfuric acid, hydrochloric acid, phosphoric acid and p-toluenesulfonic acid, and the dosage of the catalyst is 1-3% of the total mass of the raw materials.

The preparation method of the shrinkage reducing agent for the ultra-high performance concrete comprises the following steps:

(1) esterification: adding maleic anhydride, polyethylene glycol substances and polypropylene glycol substances into a reaction container, uniformly stirring, dropwise adding a catalyst within 1-2 hours, reacting at 40-70 ℃ for 4-8 hours, and cooling to room temperature to obtain a compound A solution after the reaction is finished;

(2) polymerization: and respectively dropwise adding persulfate solutions into the solution A, finishing dropwise adding within 1.5-2.5 hours, controlling the reaction temperature to be 50-60 ℃, and continuously reacting for 1-4 hours. The persulfate is any one of ammonium persulfate, potassium persulfate and sodium persulfate, and the dosage of the persulfate is 0.5 to 1 percent of that of the solution A

(3) Neutralizing: and after the reaction is finished, cooling to room temperature, and adding alkali to adjust the pH value of the solution to 6-7 to obtain the shrinkage reducing agent for the ultra-high performance concrete. The alkali is any one or more of sodium hydroxide, potassium hydroxide, diethanolamine, diethanol monoisopropanolamine, triethanolamine and triisopropanolamine.

The shrinkage reducing agent for the ultra-high performance concrete prepared by the invention has the following structure:

the preparation reaction process is as follows:

in the formula, R₁，R₂Is C1-C4 alkyl or H, can be-CH₃、-CH₂CH₃、-CH₂CH₂CH₃、-CH₂CH₂CH₂CH₃、-CH₂CHCH₃And in OH, m and n are integers, m is 5-40, n is 5-25, and a: b is 1-5.

Compared with the prior art, the invention has the advantages that:

(1) the concrete shrinkage reducing agent prepared by the invention is a water-soluble polymer, is not easy to volatilize and flammable, and is more convenient for engineering application.

(2) The concrete shrinkage reducing agent prepared by the invention has no obvious negative influence on the setting time and the later strength of the concrete.

(3) Compared with the traditional micromolecular alcohol shrinkage reducing agent, the concrete shrinkage reducing agent prepared by the invention has lower mixing amount and more obvious shrinkage reducing effect in application.

(4) The concrete shrinkage reducing agent prepared by the invention has better compatibility with the polycarboxylic acid water reducing agent and the functional auxiliary agent thereof, and the water reducing rate of the polycarboxylic acid water reducing agent is not reduced.

(5) The raw materials related by the invention are cheap and easily available, the synthetic process is simple and convenient, the environment is friendly, and the method is suitable for popularization and application.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.

Detailed Description

The present invention will be further described with reference to the following examples.

Example 1

A preparation method of a shrinkage reducing agent for ultrahigh-performance concrete comprises the following steps:

(1) adding 98g of maleic anhydride, 120g of diethylene glycol monomethyl ether and 90g of propylene glycol monomethyl ether into a reaction vessel, uniformly stirring, adding 3g of p-toluenesulfonic acid, reacting at 70 ℃ for 4 hours, and cooling to room temperature after the reaction is finished to obtain a compound A solution;

(2) adding 160g of deionized water into 40g of the solution A, carrying out water bath reaction at 60 ℃, and then dropwise adding an ammonium persulfate solution into the solution A, wherein the dropwise adding time is controlled to be 2 hours;

(3) and (3) continuing to react for 1 hour after the ammonium persulfate solution is dropwise added, cooling to room temperature after the reaction is finished, adding diethanolamine to adjust the pH value of the solution to 6-7, and obtaining the product, namely the shrinkage reducing agent for the ultra-high performance concrete.

Example 2

A preparation method of a shrinkage reducing agent for ultrahigh-performance concrete comprises the following steps:

(1) adding 98g of maleic anhydride, 60g of diethylene glycol monomethyl ether, 50g of diethylene glycol monoethyl ether and 70g of dipropylene glycol monomethyl ether into a reaction vessel, uniformly stirring, adding 1g of sulfuric acid and 1.5g of p-toluenesulfonic acid, reacting at 60 ℃ for 2 hours, and cooling to room temperature after the reaction is finished to obtain a compound A solution;

(2) adding 340g of deionized water into 60g of the solution A, carrying out water bath reaction at 60 ℃, and then dropwise adding a potassium persulfate solution into the solution A, wherein the dropwise adding time is controlled to be 1.5 hours;

(3) and (3) continuing to react for 1 hour after the potassium persulfate solution is dripped, cooling to room temperature after the reaction is finished, adding triethanolamine to adjust the pH value of the solution to 6-7, and obtaining the product, namely the shrinkage reducing agent for the ultra-high performance concrete.

Example 3

A preparation method of a shrinkage reducing agent for ultrahigh-performance concrete comprises the following steps:

(1) adding 98g of maleic anhydride, 90g of ethylene glycol monoethyl ether and 81g of dipropylene glycol monoethyl ether into a reaction container, uniformly stirring, adding 1g of hydrochloric acid and 1g of p-toluenesulfonic acid, reacting at 55 ℃ for 2 hours, and cooling to room temperature after the reaction is finished to obtain a compound A solution;

(2) adding 80g of the solution A into 240g of deionized water, carrying out water bath reaction at 55 ℃, and then dropwise adding a sodium persulfate solution into the solution A, wherein the dropwise adding time is controlled to be 1.5 hours;

(3) and (3) continuing the reaction for 1 hour after the dropwise addition of the sodium persulfate solution is finished, cooling to room temperature after the reaction is finished, adding diethanol monoisopropanolamine to adjust the pH of the solution to 6-7, and obtaining the product, namely the shrinkage reducing agent for the ultra-high performance concrete.

Example 4

A preparation method of a shrinkage reducing agent for ultrahigh-performance concrete comprises the following steps:

(1) adding 98g of maleic anhydride, 85g of polyethylene glycol monomethyl ether (Mw is 300g) and 81g of dipropylene glycol monoethyl ether into a reaction vessel, uniformly stirring, adding 1g of hydrochloric acid and 1g of p-toluenesulfonic acid, reacting at 55 ℃ for 2 hours, and cooling to room temperature after the reaction is finished to obtain a compound A solution;

(2) adding 80g of the solution A into 240g of deionized water, carrying out water bath reaction at 55 ℃, and then dropwise adding a sodium persulfate solution into the solution A, wherein the dropwise adding time is controlled to be 1.5 hours;

(3) and (3) continuing the reaction for 1 hour after the dropwise addition of the sodium persulfate solution is finished, cooling to room temperature after the reaction is finished, adding diethanol monoisopropanolamine to adjust the pH of the solution to 6-7, and obtaining the product, namely the shrinkage reducing agent for the ultra-high performance concrete.

Example 5

A preparation method of a shrinkage reducing agent for ultrahigh-performance concrete comprises the following steps:

(1) adding 98g of maleic anhydride, 95g of polypropylene glycol monoethyl ether (Mw is 800g) and 70g of dipropylene glycol monomethyl ether into a reaction vessel, uniformly stirring, adding 1g of sulfuric acid and 1g of p-toluenesulfonic acid, reacting at 55 ℃ for 2 hours, and cooling to room temperature after the reaction is finished to obtain a compound A solution;

(2) adding 80g of the solution A into 240g of deionized water, carrying out water bath reaction at 55 ℃, and then dropwise adding an ammonium persulfate solution into the solution A, wherein the dropwise adding time is controlled to be 2 hours;

(3) and (3) continuing to react for 1 hour after the ammonium persulfate solution is dropwise added, cooling to room temperature after the reaction is finished, adding triisopropanolamine, and adjusting the pH value of the solution to 6-7 to obtain the product, namely the shrinkage reducing agent for the ultrahigh-performance concrete.

Example 6

A preparation method of a shrinkage reducing agent for ultrahigh-performance concrete comprises the following steps:

(1) adding 98g of maleic anhydride, 95g of polypropylene glycol monomethyl ether (Mw is 1200g) and 75g of diethylene glycol monomethyl ether into a reaction vessel, stirring uniformly, adding 1g of sulfuric acid and 1g of phosphoric acid, reacting at 55 ℃ for 2 hours, and cooling to room temperature after the reaction is finished to obtain a compound A solution;

(2) adding 80g of the solution A into 240g of deionized water, carrying out water bath reaction at 60 ℃, and then dropwise adding a sodium persulfate solution into the solution A, wherein the dropwise adding time is controlled to be 2 hours;

(3) and (3) continuing to react for 1 hour after the dropwise addition of the sodium persulfate solution is finished, cooling to room temperature after the reaction is finished, adding a 30% sodium hydroxide aqueous solution, and adjusting the pH value of the solution to 6-7 to obtain the product, namely the shrinkage reducing agent for the ultrahigh-performance concrete.

Example 7

A preparation method of a shrinkage reducing agent for ultrahigh-performance concrete comprises the following steps:

(1) 98g of maleic anhydride and 75g of diethylene glycol monomethyl ether are added into a reaction vessel, stirred uniformly, then 1g of sulfuric acid and 1g of phosphoric acid are added, then the reaction is continued for 2 hours under stirring at 50 ℃, then 95g of polypropylene glycol monomethyl ether (Mw ═ 1200g) is added, the reaction is continued for 1 hour under stirring at 60 ℃, and after the reaction is finished, the reaction is cooled to room temperature to obtain a compound A solution.

(2) And adding 80g of the solution A into 240g of deionized water, stirring, adding 0.5g of dicyclohexylcarbodiimide after water bath at 60 ℃ for 1h, stirring for 5min, and dropwise adding a sodium persulfate solution, wherein the dropwise adding time is controlled to be 2 h. Wherein the solute content of the sodium persulfate solution was 0.8 g. Dicyclohexylcarbodiimide is a regulator and does not participate in the reaction.

(3) And (3) continuing to perform constant-temperature reaction for 1 hour after the dropwise addition of the sodium persulfate solution is finished, cooling to room temperature after the reaction is finished, adding a 30% sodium hydroxide aqueous solution, and adjusting the pH value of the solution to 6-7 to obtain the product, namely the shrinkage reducing agent for the ultrahigh-performance concrete.

Example 8

A preparation method of a shrinkage reducing agent for ultrahigh-performance concrete comprises the following steps:

(3) 98g of maleic anhydride and 75g of diethylene glycol monomethyl ether are added into a reaction vessel, stirred uniformly, then 1g of sulfuric acid and 1g of phosphoric acid are added, then the reaction is continued for 2 hours under stirring at 50 ℃, then 95g of polypropylene glycol monomethyl ether (Mw ═ 1200g) is added, the reaction is continued for 1 hour under stirring at 60 ℃, and after the reaction is finished, the reaction is cooled to room temperature to obtain a compound A solution.

(4) And adding 80g of the solution A into 240g of deionized water, stirring, carrying out water bath at 50 ℃ for 1h, adding 0.196g of thioacetamide, stirring for 5min, dropwise adding a sodium persulfate solution, and controlling the dropwise adding time to be 2 h. Wherein the solute content of the sodium persulfate solution was 0.8 g. Thioacetamide is a regulator and does not participate in the reaction.

(3) And (3) continuing to perform constant-temperature reaction for 1 hour after the dropwise addition of the sodium persulfate solution is finished, cooling to room temperature after the reaction is finished, adding a 30% sodium hydroxide aqueous solution, and adjusting the pH value of the solution to 6-7 to obtain the product, namely the shrinkage reducing agent for the ultrahigh-performance concrete.

The products prepared in the above examples 1 to 8 can be used alone as shrinkage reducing agents for ultra-high performance concrete. Or, in order to further improve the performance, when in use, the product of the invention can be used together with calcium sulfate whisker and silicon dioxide powder. Further preferably, the silica is subjected to a modification treatment in advance. The modification treatment method comprises the following steps: the modified silica is obtained by immersing a commercial silica powder in an aqueous solution containing a detergent, preferably a household kitchen dish detergent, for half an hour, followed by filtration and drying. CaSO₄The crystal whisker has toughening effect, can reduce the shrinkage of concrete and prevent the cement-based material from generating cracks. The modified silicon dioxide has better hydrophilicity and can reduce the evaporation of water in the concrete.

Application example 1

The common ultrahigh-performance concrete comprises the following components in parts by weight: 690 parts of ordinary 52.5R portland cement, 160 parts of silica fume, 210 parts of mineral powder, 1080 parts of river sand, 160 parts of steel fiber, 9 parts of water reducing agent (Cika Viscocrete-3301) and 170 parts of water.

Application example 2

The shrinkage-reducing type ultrahigh-performance concrete comprises the following components in parts by weight: 690 parts of ordinary 52.5R portland cement, 160 parts of silica fume, 210 parts of mineral powder, 1080 parts of river sand, 160 parts of steel fiber, 9 parts of water reducing agent (Cika Viscocrete-3301), 1 part of shrinkage reducing agent in example 1 and 170 parts of water.

Application example 3

The shrinkage-reducing type ultrahigh-performance concrete comprises the following components in parts by weight: 690 parts of ordinary 52.5R portland cement, 160 parts of silica fume, 210 parts of mineral powder, 1080 parts of river sand, 160 parts of steel fiber, 9 parts of water reducing agent (Cika Viscocrete-3301), 2 parts of shrinkage reducing agent in example 1 and 170 parts of water.

Application example 4

The shrinkage-reducing type ultrahigh-performance concrete comprises the following components in parts by weight: 690 parts of ordinary 52.5R portland cement, 160 parts of silica fume, 210 parts of mineral powder, 1080 parts of river sand, 160 parts of steel fiber, 9 parts of water reducing agent (Cika Viscocrete-3301), 2 parts of shrinkage reducing agent in example 2 and 170 parts of water.

Application example 5

The shrinkage-reducing type ultrahigh-performance concrete comprises the following components in parts by weight: 690 parts of ordinary 52.5R portland cement, 160 parts of silica fume, 210 parts of mineral powder, 1080 parts of river sand, 160 parts of steel fiber, 9 parts of water reducing agent (Cika Viscocrete-3301), 2 parts of shrinkage reducing agent in example 3 and 170 parts of water.

Application example 6

The shrinkage-reducing type ultrahigh-performance concrete comprises the following components in parts by weight: 690 parts of ordinary 52.5R portland cement, 160 parts of silica fume, 210 parts of mineral powder, 1080 parts of river sand, 160 parts of steel fiber, 9 parts of water reducing agent (Cika Viscocrete-3301), 2 parts of shrinkage reducing agent in example 4 and 170 parts of water.

Application example 7

The shrinkage-reducing type ultrahigh-performance concrete comprises the following components in parts by weight: 690 parts of ordinary 52.5R portland cement, 160 parts of silica fume, 210 parts of mineral powder, 1080 parts of river sand, 160 parts of steel fiber, 9 parts of water reducing agent (Cika Viscocrete-3301), 2 parts of shrinkage reducing agent in example 6 and 170 parts of water.

Application example 8

The shrinkage-reducing type ultrahigh-performance concrete comprises the following components in parts by weight: 690 parts of ordinary 52.5R portland cement, 160 parts of silica fume, 210 parts of mineral powder, 1080 parts of river sand, 160 parts of steel fiber, 9 parts of water reducing agent (Cika Viscocrete-3301), 2 parts of shrinkage reducing agent in example 7 and 170 parts of water.

Application example 9

The shrinkage-reducing type ultrahigh-performance concrete comprises the following components in parts by weight: 690 parts of ordinary 52.5R portland cement, 160 parts of silica fume, 210 parts of mineral powder, 1080 parts of river sand, 160 parts of steel fiber, 9 parts of water reducing agent (Cika Viscocrete-3301), 2 parts of shrinkage reducing agent in example 8 and 170 parts of water.

Application example 10

The shrinkage-reducing type ultrahigh-performance concrete comprises the following components in parts by weight: 690 parts of ordinary 52.5R portland cement, 160 parts of silica fume, 210 parts of mineral powder, 1080 parts of river sand, 160 parts of steel fibers, 9 parts of a water reducing agent (Cika Viscocrete-3301), 2 parts of a shrinkage reducing agent in example 6, 170 parts of water, 2 parts of calcium sulfate whiskers and 1 part of silicon dioxide powder.

Application example 11

The shrinkage-reducing type ultrahigh-performance concrete comprises the following components in parts by weight: 690 parts of ordinary 52.5R portland cement, 160 parts of silica fume, 210 parts of mineral powder, 1080 parts of river sand, 160 parts of steel fibers, 9 parts of a water reducing agent (Cika Viscocrete-3301), 2 parts of a shrinkage reducing agent in example 8, 170 parts of water, 2 parts of calcium sulfate whiskers and 1 part of silicon dioxide powder.

Mixing and stirring the concrete materials of application examples 1-11 according to the following steps:

(1) carrying out vibration stirring dispersion on cement, silica fume, mineral powder and river sand to prepare ultrahigh-performance concrete dry powder with good homogeneity;

(2) pouring the ultrahigh-performance concrete dry powder into a common forced mixer, adding weighed water, a water reducing agent (Cika Viscocrete-3301) and a shrinkage reducing agent, and stirring for 3-5 minutes to obtain a slurry material;

(3) uniformly adding the weighed steel fibers into the slurry material, stirring while adding to ensure that the steel fibers are not agglomerated, and stirring for 2-4 minutes to prepare the ultra-high performance concrete slurry;

(4) pouring and forming, namely placing the prepared ultra-high performance concrete slurry into a mould in a pouring mode, testing the concrete setting time according to GB/T50080-2016 standard of common concrete mixture performance test method, and removing the mould after the slurry is hardened to obtain a test piece;

(5) curing the test piece under the condition of a standard concrete curing system at the room temperature of 20 +/-2 ℃; the humidity is not less than 95%.

After stirring, forming a concrete compressive strength test piece of 100mm multiplied by 100mm, a concrete flexural strength test piece of 100mm multiplied by 400mm, a concrete shrinkage prism test piece of 100mm multiplied by 515mm, after the slurry is hardened, removing the mould and placing the test piece in a standard curing room for curing, respectively marking the compressive strength and the flexural strength of the ultra-high performance concrete to the corresponding age testing strength, taking the ultra-high performance concrete shrinkage test piece out of the standard curing room after marking for 3 days, immediately moving the test piece into a constant temperature and humidity room to measure the initial length of the test piece, measuring the shrinkage value according to 7 days, 28 days and 60 days, and obtaining the performance testing result shown in table 1.

TABLE 1 Effect of shrinkage reducing Agents on compression, flexural Strength and shrinkage

As shown in the results of Table 1, the shrinkage reducing agent prepared by the example of the invention has no obvious negative effect on the setting time, the compressive strength and the flexural strength of the ultra-high performance concrete compared with the reference sample, but can significantly reduce the total shrinkage of the ultra-high performance concrete, and the shrinkage of 7d, 28d and 60d is lower than that of the reference group.

Claims (9)

1. A shrinkage reducing agent for ultrahigh-performance concrete is characterized by being prepared from maleic anhydride, polyethylene glycol substances and polypropylene glycol substances serving as raw materials through esterification and polymerization reactions, wherein the molar ratio of the maleic anhydride to the polyethylene glycol substances to the polypropylene glycol substances is 1:1: 0.2-1: 2: 0.5.

2. The shrinkage reducing agent for ultra-high performance concrete according to claim 1, wherein the polyethylene glycol is polypropylene glycol and derivatives thereof.

3. The shrinkage reducing agent for ultra-high performance concrete according to claim 2, wherein the polyethylene glycol derivative is one of polyethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and triethylene glycol monomethyl ether.

4. A shrinkage reducing agent for ultra-high performance concrete, according to claim 1, wherein the polypropylene glycol-based substance is polypropylene glycol and a derivative thereof.

5. The shrinkage reducing agent for ultra-high performance concrete according to claim 4, wherein the polypropylene glycol derivative is one of polypropylene glycol monomethyl ether, dipropylene glycol monoethyl ether and dipropylene glycol monobutyl ether.

6. The shrinkage reducing agent for ultra-high performance concrete as claimed in claim 1, wherein the catalyst is one of sulfuric acid, hydrochloric acid, phosphoric acid and p-toluenesulfonic acid, and the amount of the catalyst is 1-3% of the total mass of the raw materials.

7. A method for preparing a shrinkage reducing agent for ultra-high performance concrete according to any one of claims 1 to 6, comprising the steps of:

(1) esterification: adding maleic anhydride, polyethylene glycol substances and polypropylene glycol substances into a reaction container, uniformly stirring, dropwise adding a catalyst within 1-2 hours, reacting at 40-70 ℃ for 4-8 hours, and cooling to room temperature to obtain a compound A solution after the reaction is finished;

(2) polymerization: respectively dropwise adding persulfate solutions into the solution A within 1.5-2.5 hours, controlling the reaction temperature to be 50-60 ℃, and continuously reacting for 1-4 hours;

(3) neutralizing: and after the reaction is finished, cooling to room temperature, and adding alkali to adjust the pH value of the solution to 6-7 to obtain the shrinkage reducing agent for the ultra-high performance concrete.

8. The method of claim 7, wherein the persulfate is one of ammonium persulfate, potassium persulfate and sodium persulfate, and the amount of the persulfate is 0.5-1% of that of the solution A.

9. The method of claim 7, wherein the alkali is one or more of sodium hydroxide, potassium hydroxide, diethanolamine, diethanolisopropanolamine, triethanolamine, and triisopropanolamine.